Character select indicator for typewriter

ABSTRACT

An electrical character select indicator for a typewriter where the latch interposers of a typical single printing head typewriter of the IBM Selectric type are each coupled to a differential transformer through a linkage which is coupled to the latch interposers, the differential transformer having a core which in its null position indicates the latch interposer is unactivated and when moved by the latch interposer means causes the differential transformer to provide an output voltage to indicate actuation of the latch interposer.

[451 July 25,1972

Holmes,

[54] CHARACTER SELECT INDICATOR FOR TYPEWRITER [72] Inventor: William C. Bennett, Menlo Park, Calif. Primaw Examiner kobert E. Pulfrey Novar Corporation, Mountain View, Calif. Assistant Examiner-Clifford D. Crowder July 17, 1970 [73] Assignee:

[22] Filed:

Attorney-Theodore C. Jay, Jr., Norman J. OMalley and John F. Lawler [2]] Appl. No.:

626 03 //Il 73 926 1. 3 3 94.- M3,... 0 m m "5/ 7 U9 B 52 user...

ferential transformer through a linkage which is coupled to the latch interposers, the differential transformer having a core References Cited UNITED STATES PATENTS which in its null position indicates the latch interposer is unac tivated and when moved by the latch interposer means causes 7/1969 1 1/1965 12/ 1968 L J S e m o H the differential transformer to provide an output voltage to indicate actuation of the latch interposer.

L a t e t n a r G .L a t e n e s d u n K w e k c R 1 Claim, 3 Drawing Figures CHARACTER SELECT INDICATOR FOR TYPEWRITER BACKGROUND OF THE INVENTION This invention relates to typewriter, and more particularly to an electrical character select indicator for the typewriter.

The present invention is an improvement in a typewriter of the type where a plurality of characters are arranged on a single printing head. This is illustrated in US. Pat. No. 2,919,002 issued to LB. Palmer, Dec. 29, 1959. One such typewriter is designated by the trademark IBM SELECTRIC.

In general, the pressing of a key button positions a character in the printing position by rotating and tilting the printing head predetermined angles. The amount of tilt or rotation is in general determined by the typewriter mechanism mechanically decoding what is in effect a binary six bit code. In other words, when a type button is pressed, a unique combination of six levers is in effect actuated. These levers are mechanically coupled to the printing head in such a manner that the six bit binary lever code is decoded by the linkage of the printing head to tilt and rotate it to a character position.

It is, of course, obvious that an electrical readout of the specific character selected can be obtained by sensing this six bit binary code. This has been done in the past by coupling open leaf contact switches to certain levers to detect their movement; alsoby fastening a magnet to these levers, movement of the magnet actuating a reed switch. Both of these structures require frequent adjustment and they are unreliable.

OBJECTS AND SUMMARY OF THE INVENTION It is, therefore, a general object of the present invention to provide an improved character select indicator for a typewriter.

It is another object of the invention to provide an indicator of the above type which is simple and reliable in operation.

ln'accordance with the above objects the present invention relates to a typewriter having a printing head with a plurality of characters arranged thereon and operable by a corresponding plurality of type keys to present one character at a time to a printing position. Selector interposer means are provided for each of the type keys. Each of the interposer means has a plurality of selector lugs uniquely positioned forming notches. A plurality of latch interposer means having single lugs are also provided. A plurality of selector bails are included which extend through the notches. Each of the bails also extend in front of a lug of an associated latch interposer means. Actuation of a key initiates movement of an associated selector interposer means which in turn moves a combination of the bails determined by the unique lugs. The bails move into contact with the lugs of the latch interposer means to move such means. Selector latch means are coupled to the latch interposer means and to the printing head and are responsive to movement of a predetermined combination of the latch interposer means to effective selective rotation of the printing head.

The improvement of the present invention comprises a plurality of link means coupled to the latch interposer means and mounted for movement with such means. A plurality of differential transformer means are provided including reel means having primary and secondary windings thereon and a central cylindrical passage. The transformer also includes a cylindrical core coupled to the link means and movable within the passage in response to movement of the link means from a first rest position in which a first electrical output level is provided by the windings and a second actuated position in which a second electrical output level is provided. Thus, the output levels of the plurality of transformers indicate the character selected by a type key.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a portion of a typewriter in which the invention is incorporated;

FIG. 2 is an enlarged and more detailed view of a portion of FIG. 1; and

FIG. 3 is a block diagram electrical circuit used to practice the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, several of the components shown are generally like those disclosed in the Palmer patent mentioned above. This typewriter includes a representative key button 10 mounted on a key lever 11 which is pivoted on a rod 12. The key button and lever are, of course, associated with a specific character. Attached to each key lever 11 is a key lever pawl 13 which is held in its rest position by a spring 14. Pawl 13 extends below and is formed under the key lever in a position to strike the top of a selector interposer 16.

The purpose of interposer 16 is to select the amount of tilt I and rotation needed to bring the desired character to its printing position. A large fulcrumed rod 17 passes through an elongated hole in the front of each interposer lever (only one of which is, of course, shown in FIG. I) and provides the support on which the interposers pivot and slide.

The interposers 16 have several lugs 18 extending from them each with its own operation to perform. The absence or presence of these lugs in different position combinations makes each interposer unique. One lug 18a is common to all interposers its purpose being to initiate the operation cycle whenever a key lever is depressed. This is accomplished by a cycle ball 19 which is directly beneath lug 1811 which when key button 10 is pressed caused the pawl 13 to move interposer l6 and thereupon lug 18a actuates the cycle bail 19 to initiate the cycle of operation of the typewriter for that particular character selected. 2

Part of the cycle of operation is the rotation of a filter shaft 21. When interposer 16 is depressed the rear of the interposer is moved down in front of one blade of the filter shaft and as the filter shaft turns the blade drives the interposer forward to ultimately operate the character selection mechanism.

Six selector bails, two of which 22 and 23 are shown, extend through the notches formed by lugs 18 and also in front of lugs 24a and 26a of character selector latch interposers 24 and 26. Movement of interposer l6 forward as shown by arrow 27 by filter shaft 21 moves selector bails 22 and 23 forward to move forward the associated latch interposers 24 and 26. It is, of course, assumed that in this example interposer 16 would not have lugs for any of the other bails. The bails 22 and 23 and, of

course, the other four bails (not shown) and the latch interposers (only two of which are shown) are paired so that each bail operates only one latch interposer. Extension springs 24b and 2612 at the bottom of each latch interposer loads the interposer and its selector bail to the rear.

Adjustable link means 240 and 26c couple each latch interposer to selector latches 28 and 29. These selector latches are ultimately coupled to the printing head of the typewriter in a manner well illustrated in the Palmer patent to effect the proper angle of rotation and tilting. When a latch interposer is moved forward the selector latch connected to that interposer is pulled forward. Thus, whether or not a latch 28 or 29 along with the other four latches (not shown) is pulled forward is in effect a six bit binary code. As shown in the Palmer patent a predetermined combination of movements of the latch interposers 24 and 26 and the other latch interposers effect selective rotation of the printing head.

In accordance with the present invention a plurality of link means 31 and 32 (and four additional, not shown) are coupled to the latch interposers 24 and 26, respectively, and mounted for movement with the interposers. Links 31 and 32 are also coupled to differential transformers 33 and 34. In general the transformers have first and second electrical output levels which are indicative of the two positions of links 31 and 32 and their associated latch interposers 24 and 26.

FIG. 2 is a more detailed showing of the foregoing where the latch interposer 24 includes a hooked end 24d slidably mounted through a support 36 fastened to a framing member 37. Link 31 includes an end 31a also adapted for movement through retaining member 36. End 31a also abuts against hooked end 24d and is actually biased against it by a coiled spring 38, which is coaxial with a core 47. Spring 38 has one end terminated at the end 31b of the link 31 and the other end is against a framing member 39 on which the differential transformer 33 is mounted.

Referring now also to FIG. 3, the differential transformer 33 includes a reel means 41 having a primary winding 42 mounted thereon and secondary windings 43 and 44. The center primary winding is excited by a high frequency ac signal source 46 and coupled to the two secondary windings 43 and 44 which are connected series-opposing as shown by the two black dots. A core 47 which is cylindrical is movable within the cylindrical passage 48 in the reel 41 and is coupled to link 31. In its first or rest position as illustrated in FIG. 3 the core is located in a dead center position within the central passage way. Here the alternating field generated by the primary winding 42 couples equally to the secondaries 43 and 44. Thus, the voltages induced within the two secondaries are equal and opposite and the net output from the transformer is zero or nulled.

If bail 22 moves latch interposer 24 and thus the link 31, core 47 is moved in the direction shown by the arrow 49 away from the null position and more voltage will be induced in one secondary and less in the other. There will now be a net ac voltage at the output terminals 50 whose magnitude will be a function of the distance that the core is displaced from the null position. This voltage is rectified by rectifier 51, integrated by integrator 52, and amplified by amplifier 53 to produce a digital output on terminal 54. The circuit of 53, is, of course, representative of one of six circuits and the combination of the digital outputs is thus indicative of the character selected by the type key.

With the particular arrangement described in FIGS. 2 and 3 an indication of the movement of each latch interposer is reliably provided. At the same time there is a minimum of extra mechanical linkages attached to the existing character select mechanism in order to provide an electrical indication of movement. Specifically, only the simple link 31 is necessary. This provides for very little added load to the mechanical system.

At the same time, the electrical output of the differential transformer provides an accurate unambiguous indication of the mechanical position of the latch interposer. This is especially true in view of the null indication of the rest position of the latch interposer and the large magnitude voltage produced by the differential action of the transformer when the latch interposer is actuated.

I claim:

1. In a typewriter having a printing head with a plurality of characters arranged thereon and operable by a corresponding plurality of type keys to present one character at a time to a printing position, selector interposer means for each of said type keys, each of such interposer means having a plurality of selector lugs uniquely positioned forming notches, a plurality of selector lugs uniquely positioned forming notches, a plurality of latch interposer means having single lugs, a plurality of selector bails extending through said notches, each of said bails extending in front of a lug of an associated latch interposer means, actuation of a key initiating movement of an associated selector interposer means which in turn moves a combination of said bails determined by said unique lugs, said bails moving into contact with said lugs ofsaid latch interposer means to move such means, selector latch means coupled to said latch interposer means and to said printing head and responsive to movement of a predetermined combination of said latch interposer means to effect selective rotation of said printing head wherein the improvement comprises: a plurality of link means coupled to said latch interposer means and mounted for movement with such means, a plurality of differential transformer means including reel means having primary and secondary windings thereon and a central cylindrical passa e and a cylindrical core coupled to said link means and mova le within said passage in response to movement of said link means from a first rest position in which a first electrical output level is provided by said windings and a second actuated position in which a second electrical output level is provided, whereby the output levels of a plurality of said transformers indicate the character selected by said type key, said latch interposer means including one end mounted for movement in a bracket, said link means including one end mounted for movement in said bracket for contacting said end of said latch interposer means, said link means also including a second end coupled to said core, and spring biasing means coaxial with said core for biasing said first end of said link against said end of said latch interposer means. 

1. In a typewriter having a printing head with a plurality of characters arranged thereon and operable by a corresponding plurality of type keys to present one character at a time to a printing position, selector interposer means for each of said type keys, each of such interposer means having a plurality of selector lugs uniquely positioned forming notches, a plurality of selector lugs uniquely positioned forming notches, a plurality of latch interposer means having single lugs, a plurality of selector bails extending through said notches, each of said bails extending in front of a lug of an associated latch interposer means, actuation of a key initiating movement of an associated selector interposer means which in turn moves a combination of said bails determined by said unique lugs, said bails moving into contact with said lugs of said latch interposer means to move such means, selector latch means coupled to said latch interposer means and to said printing head and responsive to movement of a predetermined combination of said latch interposer means to effect selective rotation of said printing head wherein the improvement comprises: a plurality of link means coupled to said latch interposer means and mounted for movement with such means, a plurality of differential transformer means including reel means having primary and secondary windings thereon and a central cylindrical passage and a cylindrical core coupled to said link means and movable within said passage in response to movement of said link means from a first rest position in which a first electrical output level is provided by said windings and a second actuated position in which a second electrical output level is provided, whereby the output levels of a plurality of said transformers indicate the character selected by said type key, said latch interposer means including one end mounted for movement in a bracket, said link means including one end mounted for movement in said bracket for contacting said end of said latch interposer means, said link means also including a second end coupled to said core, and spring biasing means coaxial with said core for biasing said first end of said link against said end of said latch interposer means. 